**This will only work if you purchased it before the 11th. If you didn't, this may not work for you.**
Simply contact Xbox Support, whether its phone or chat. When you connect with someone, tell them you aren't happy due to the HDTV requirement for splitscreen. Tell them you wanted to play with someone and cannot since you weren't informed of the requirement.
They should issue a refund pretty fast. Mine came within 5 minutes or so of being in the chat.
The agent should credit you 1600MSP for the game and you'll be set. Remember, this will only work if you bought it before the 15th. You can still try, but it might not work.